1. Field of the Invention
The present invention relates to golf clubs and, more specifically, a golf club head and weighting method to provide better performance, greater weighting flexibility and lower production costs.
2. Description of the Related Art
The location and distribution of weight within a golf club is an important factor in the performance of the golf club. In particular, weight placement at the bottom of the golf club head provides a low center of gravity to help propel a golf ball into the air during impact, and weight concentrated at the toe and heel of the golf club head provides a resistance to twisting, or high moment of inertia, during golf ball impact. Both the low center of gravity and high moment of inertia are important performance variables which affect playability and feel of the golf club. Alternative designs have resulted in many innovations for varying the weight location and distribution in a golf club head portion. Among these designs is a combination of high and low density materials within the golf club head, and associated methods for combining these materials.
One example of multiple materials used in the construction of the golf club head is a high density material attached to a lower density material golf club head. A high density block or contoured shape is attached, via mechanical means such as friction fit, fasteners or screws, to a reciprocal recess in the golf club head, as shown in U.S. Pat. No. 5,776,010, issued to Helmstetter et al. Although supplying the desired performance enhancements, the high density block and the reciprocal recess must be machined to precise tolerances, involving high production costs.
Another example of weighting the golf club is pouring a high density fluid into a reservoir within the golf club. This ensures an exact placement of the weighting material within the golf club, as the fluid will conform to the internal shape of the reservoir without the need for mechanical or an adhesive bonding. One drawback of this type of processing is the requirement that one must operate below the melt or softening temperature of the club head material. In addition, as processing temperatures increase the associated costs will increase to accommodate higher energy use and high temperature equipment. The limitations for a low melt temperature, yet high density, material restricts the available options for this type of process.
To overcome the limitations associated with a single material, the advent of multi-component weighting systems makes use of the high density materials in combination with a carrier fluid, such as a polymer. A particulate form of the high density material is mixed with the carrier fluid and poured into the reservoir in the golf club, wherein the carrier fluid is allowed to solidify to form a composite weighting material. Readily available materials include a thermoset polymer carrier fluid, such as epoxy, which allows ambient temperature processing and solidification of the high density material and epoxy mixture. A thermoplastic polymer carrier fluid, such as polypropylene, requires heat to obtain a fluid state and cools to a solid at ambient temperatures, with the capability to be re-heated to the fluid state, in distinction to the epoxy. A disadvantage of the multi-component weighting system is the low density associated with the carrier fluid, typically 1 g/cm.sup.3, thus requiring a high ratio of the weighting material to the carrier fluid to obtain the desired high density for a bi-material weight. The carrier fluid also acts as a binder for the weighting material to ensure the bi-material weight forms a solid block.
A drawback to the multi-component weighting system is the need to use small amounts of carrier fluid relative to the weighting material, leading to entrapped air or voids and incomplete binding in the bi-material weight. Incorporating larger amounts of the carrier fluid promotes better mixing within the bi-material weight in conjunction with an attendant decrease in density. Therefore, it is desirable to provide a bi-material weight containing a higher density carrier fluid to provide greater weighting flexibility for allocating weight within a golf club head in conjunction with lower cost production. It is further desirable to provide a golf club head to accommodate the bi-material weight and enable a variable location of the bi-material weight.